docs: def _extract_obo_synonyms(rawterm):
          """Extract the synonyms defined in the rawterm.
          """
          synonyms = set()
          # keys in rawterm that define a synonym
          keys = set(owl_synonyms).intersection(rawterm.keys())
          for k in keys:
              for s in rawterm[k]:
                  synonyms.add(Synonym(s, owl_synonyms[k]))
          return synonyms